Rain sensor, in particular for a motor vehicle having a window-wiper device, and method for controlling a windshield-wiper device

ABSTRACT

A rain sensor, in particular for a motor vehicle including a window-wiper device (windshield-wiper device), including a measuring element, which has a sensitivity that is predefinable by a control device, a signal, characterizing the speed of the motor vehicle, being able to be transmitted to the control device, and the control device increasing the sensitivity of the measuring element at lower speed. Furthermore, a method for controlling a windshield-wiper device, in particular for a motor vehicle. A measuring element is connected to a control device, its sensitivity being predefined by the control device. A signal characterizing a speed of the motor vehicle is transmitted to the control device and the sensitivity of the measuring element increased at lower speed.

FIELD OF THE INVENTION

The present invention relates to a rain sensor, in particular for amotor vehicle including a window-wiper device (windshield-wiper device),and to a method for controlling a windshield-wiper device.

BACKGROUND INFORMATION

There are believed to be rain sensors for motor vehicles includingwindshield-wiper devices. These devices including a measuring element,which has a sensitivity that is predefinable by a control device. Forinstance, German Published Patent Application No. 197 23 859 refers to arain sensor in which day and night may be distinguished with the aid ofa photocell and the triggering sensitivity of the rain sensor iscontrolled. Furthermore, the sensitivity of the measuring element of therain sensor may be varied as a function of the detected signal, and,thus, the rain intensity.

SUMMARY OF THE INVENTION

The rain sensor according to the present invention may provide that thesensitivity of the measuring element of the rain sensor is controllableas a function of the motor vehicle speed, and that a higher sensitivityof the measuring element may be adjusted, especially at lower speeds. Inthis manner, the subjective sensitivity of the rain sensor may beimproved, since the airstream, at lower speeds, does not bring about aneffect that may allow the drops to break up.

The sensitivity may be increased when the speed is very low, especiallybelow 5 km/h or even less than 3 km/h. In this case, the sensitivity isalready increased when, for example, the car is driven at very low speedin stalled traffic or at a traffic light, thereby resulting in animproved wiping characteristic.

If the control device has a single wiping stage in which a single wipingcycle may be activated in each case, and if the sensitivity is increasedin this operating step, a wiping performance results that adapts in aparticularly sensitive manner.

The control device may increase the sensitivity in those instances whena longer period of time, specifically at least5 seconds, has elapsedsince the last wiping cycle. In this manner, a build-up on the windowduring longer wiping intervals is prevented in an especially effectivemanner.

The exemplary method according to the present invention may provide thata signal characterizing the speed is transmitted to the control deviceand the sensitivity of the measuring element is increased at low speed.In this manner, a sensitivity is attained that is subjectively moreeven.

An increase in the sensitivity when the speed is low, in particular lessthan 5 km/h or even less than 3 km/h, prevents a disruptive “build-up”on the window at lower speeds. When the windshield-wiper deviceimplements single wiping cycles and increases the sensitivity betweenthe single wiping cycles, the wiping performance is effectively improvedfor the driver.

The sensitivity may be increased once a longer time interval of, inparticular, at least 5 seconds has elapsed since the last wiping cycle,in order to always have a clean window available when the rainquantities are low and the vehicle is stopped at a traffic light orcaught in backed-up traffic.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic representation of a rain sensor according tothe present invention.

FIG. 2 a shows an example of a speed characteristic curve above thetime.

FIG. 2 b shows a sensitivity profile over the time, corresponding toFIG. 2 a.

FIG. 3 a shows an example of a speed profile over the time.

FIG. 3 b shows the wiping activity over the time, in a profile accordingto FIG. 3 a.

FIG. 3 c shows the sensitivity over the time corresponding to a speedprofile from FIG. 3 a.

DETAILED DESCRIPTION

In a schematic representation, FIG. 1 shows a rain sensor 10 configuredaccording to an exemplary embodiment of the present invention. Itincludes a measuring element 12, which is able to detect moisture on awindow 14, in particular the windshield of a motor vehicle. Measuringelement 12 is connected to a control device 16, which is also connectedto a speedometer device (not shown here). This speedometer devicetransmits to control device 16 a signal characterizing speed v of themotor vehicle. Furthermore, control device 16 is connected to awindshield-wiper device 18, which includes at least one windshield wiper20, which swipes across window 14 during operation and squeezes moistureoff this window. Typically, measuring element 12 is arranged in theregion of window 14 across which wiper 20 swipes.

According to the exemplary embodiment of the present invention, controldevice 16 is configured or arranged such that a transmitting diodecouples light into window 14, which, on a dry window, is totallyreflected and focused onto a receiver, . . . sensitivity E of measuringelement 12 is able to be predefined. In the case of optical sensors,this may be implemented, for instance, in that the transmitting capacityof the transmitting diode is increased, or the temperature sensitivity,i.e., the follow-up speed of the reference value, is slowed tocompensate for temperature-dependent signal changes.

FIG. 2 a shows a speed characteristic curve above the time by manner ofexample, with the proviso that signal v is proportional to the vehiclespeed. Correspondingly to the speed characteristic curve of FIG. 2 a,FIG. 2 b plots sensitivity E of measuring element 12. In a first rangeI, the speed remains constant and sensitivity E is therefore constant aswell. In a second range II, the speed drops and sensitivity E ofmeasuring element 12 rises correspondingly. In a third range, the speedis constant again, but lower than in the first range. Correspondingly,sensitivity E of measuring element 12 is constant in the third range andat a higher level than in the first range. For the fourth range, thesame applies as for the second range, the same as for the first andthird range holds for the fifth range, but here the speed is at an evenlower level, so that sensitivity E attains a maximum value as well.

FIG. 3 a shows the speed profile above the time by manner of example. InFIG. 3 b, the wiping activity of windshield wiper 20 is drawn in abovethe time, each peak representing a performed wiping cycle. FIG. 3 cshows sensitivity E above the time.

In a first range I, the motor vehicle drives at a speed v1, subsequentlyslows down, but then continues at a speed v2, whereupon it again slowsdown somewhat until coming to a standstill. During this entire time, thewiping activity remains basically constant. A new wiping cycle istriggered every three seconds, for example. The reason for this is that,due to the airstream, moisture droplets continually appear in thedetection area of measuring element 12, thereby regularly triggeringwiping cycles. In second range II, the motor vehicle is at rest. Sincemoisture droplets from the airstream no longer drift into the region ofmeasuring element 12, a longer wiping interval occurs, for instance ofapproximately 5 seconds. Control device 16 thereupon increases thesensitivity (E), as may be seen in FIG. 3 c. In this third range III,sensitivity E is increased to such a degree that the wiping activitycorresponds roughly to the wiping activity of first range I. In thismanner, the driver obtains a more even wiping profile.

1. A rain sensor for a motor vehicle including a wiper device, the rainsensor comprising: a control device; and a measuring element having asensitivity that is predefinable by the control device; wherein a signalcharacterizing a speed of the motor vehicle is transmittable to thecontrol device, and wherein the control device increases the sensitivityof the measuring element at a lower speed; wherein the control devicehas a single wiping stage in which a single wiping cycle is activatablein each case, and the sensitivity of the measuring element is increasedin the single wiping cycle; and wherein the control device increases thesensitivity of the measuring element when a longer time interval haselapsed since a last wiping cycle.
 2. The rain sensor of claim 1,wherein the control device increases the sensitivity when the speed islow.
 3. The rain sensor of claim 1, wherein the control device increasesthe sensitivity when the speed is less than 5 km/h.
 4. The rain sensorof claim 1, wherein the control device increases the sensitivity whenthe speed is less than 3 km/h.
 5. The rain sensor of claim 1, whereinthe longer time interval is at least 5 seconds.
 6. A method forcontrolling a window-wiper device for a motor vehicle including ameasuring element that has a sensitivity predefined by a control device,the method comprising: transmitting a signal characterizing a speed ofthe motor vehicle to the control device; and increasing the sensitivityof the measuring element at lower speed; wherein the windshield-wiperdevice implements single wiping cycles and the sensitivity of themeasuring element is increased between the single wiping cycles; andwherein the sensitivity of the measuring element is increased when alonger time interval has elapsed since the last wiping cycle.
 7. Themethod of claim 6, wherein the sensitivity of the measuring element isincreased when the speed is low.
 8. The method of claim 6, wherein thesensitivity of the measuring element is increased when the speed is lessthan 5 km/h.
 9. The method of claim 6, wherein the sensitivity of themeasuring element is increased when the speed is less than 3 km/h. 10.The method of claim 6, wherein the longer time interval is at least 5seconds.